Syntheses And Properties Of Low-dimensional Multifunctional Magnetic Complexes

The design and study of multifunctional materials have attracted a great deal of attention due to their fundamental interests and their potential applications. Based on molecule-based magnets, one or more physical properties, such as chirality, optical activity, porosity, conductivity, or ferroelectricty are possible introduced in one molecule. For instance, the synthesis of molecular materials with multiferroic and magnetic properties has been one of the most important challenges of the last few years. On the other hand, the 4d- or 5d-based single-molecule magnets (SMMs) and single-chain magnets (SCMs) play an important role in the field of molecular magnets. They have strong magnetic exchange which can build molecular-based magnets with high critical temperatures, and they have strong anisotropy which is good for high anisotropic molecular magnets. For their uniqe properties, they have potential applications such as high density magnetic storage, memories, sensors, quantum computing applications and more recently for spintronics.Cyanide preference for binding just two metal centers, one at each end, to afford a linear bridging arrangement is well-established. The prediction of the nature of the magnetic coupling makes the cyanide ion become one of the optimal bridging ligands for constructing magnetic materials. In this thesis, we are working on the design, syntheses and magneto-structural studies of new cyano-bridge chiral magnets such as single-molecule magnets and single-chain magnets, chiral spin-crossover complexes with novel structures and functional properties.1. Two couples of enantiomerically pure chiral cyano-bridged heterobimetallic one-dimensional (1D) chain complexes:[Mn((R,R)-salcy)Ru(salen)(CN)2]n (1, Salcy=N,N’-(1,2-cyclohexanediylethylene)bis(salicylideneiminato) dianion), [Mn((S,S)-salcy)Ru(salen)(CN)2]n (2), [Mn((R,R)-salphen)Ru(salen)(CN)2]n (3, salphen=N,N’-(1,2-diphenylethylene)bis(salicylideneiminato) dianion)), and [Mn((S,S)-salphen)Ru(salen)(CN)2]n (4) have been successfully synthesized by the reactions of MnⅢ schiff-base complexes with the dicyanometalate building block, [Ru(salen)(CN)2] (salen2-=N,N’-ethylenebis(salicylideneimine) dianion). Circular dichroism and vibrational circular dichroism (VCD) spectra confirm the enantiomeric nature of the optically active complexes. Structural analyses reveal the formation of neutral cyano-bridged zigzag single chains in 1 and 2, and double chains in 3 and 4, respectively. Magnetic studies show that antiferromagnetic coupling are operative between RuⅢ and MnⅢ centers bridged by cyanide. Compounds 1 and 2 show metamagnetic behavior with a critical field of about 7.2 kOe at 1.9 K resulted from the intermolecular π…π interactions.2. Four couples of enantiomerically pure chiral cyano-bridged heterobimetallic complexes:[Mn(salen)Ru((R,R)-(5-Cl-salcy))(CN)2]n (5), [Mn(salen)Ru((S,S)-(5-Cl-salcy))(CN)2]n (6), [Mn(salen)Ru((R,R)-(5-Br-salcy))(CN)2]n (7), [Mn(salen)Ru((S,S)-(5-Br-salcy))(CN)2]n (8), [Ni(tren)(Ru((R,R)-(5-Cl-salcy))(CN)2)2] (9, tren=tri(2-aminoethyl)amine)), [Ni(tren)(Ru((S,S)-(5-Cl-salcy))(CN)2)2] (10), [Cu(R,R-chxn)(Ru((R,R)-(5-Cl-salcy))(CN)2)2] (11, chxn= (R,R)-1,2-Diaminocyclohexane), and [Cu(chxn)(Ru((S,S)-(5-Cl-salcy))(CN)2)2] (12). have been successfully synthesized by the reactions of MnⅢ schiff-base complexes with the dicyanometalate building block, (R,R)/(S,S) [Ru(5-X-salcy)](CN)2] (salcy2-=N,N’-(1,2-cyclohexanediylethylene)bis (salicylideneiminato) dianion), X=Cl, Br). Circular dichroism and vibrational circular dichroism (VCD) spectra confirm the enantiomeric nature of the optically active complexes. Magnetic studies demonstrate that antiferromagnetic interactions are operative in complexes 5-8. With the bending of the Mn-N=C angles, the ferromagnetic couplings become weak while the antiferromagnetic interactions become strong in the chains. Ferromagnetic couplings are operative between RuⅢ and NiⅡ/CuⅡ centers bridged by cyanide in complexes 9-12. Complexes 5 and 7 exhibit slow magnetic relaxation in the absence of an applied dc field with To= 5.63×10-10 s, △Eeff/kB=28.2 K; τo= 6.14×10-6 s, △Eeff/kB=16.9 K.3. Using the new dicyano building bolck [Ru(L’)(CN)2]" (L’= 2’-hydroxyacetophenone imine), five one-dimentinal cyano-bridged heterobimetallic complexes: [Mn(salen)Ru(L’)(CN)2]n (13), [Mn(salcy)Ru(L’)(CN)2]n (14), [Mn(nappa)Ru(L’)(CN)2]n (15, nappa= N,N’-(1-methylethylene)bis(2-hydroxynaphthalene-1-carbaldehydene-iminate)dia nion), [Mn(napcy)Ru(L’)(CN)2]n (16, napcy=N,N’-(1,2-cyclohexanediylethylene) bis (2-hydroxynaphthalene-l-carbaldehydene-iminate) dianion), [Cu(chxn)2 Ru(L’)(CN)2]n (17, chxn=1,2-Diaminocyclohexane), have been synthesized and structurally characterized. The magnetic properties and magneto-structural correlation in this system are investigated. Magnetic studies demonstrate that antiferromagnetic interactions are operative in complexes 13 and 14. With the bending of the Mn-N≡C angles, the ferromagnetic couplings become weak while the antiferromagnetic interactions become strong in the chains. Ferromagnetic couplings are operative between RuⅢ and MnⅢ centers bridged by cyanide in complexes 15 and 16. Complex 17 exhibits very weak antiferromagnetic coupling in cyano-bridge compounds.4. Using L1R, L1S, L2R, L2S (L1=(R)/(S)-4,5-pinenepyridyl-2-pyridine(L1R/L1S); L2= (R)/(S)-4,5-pinenepyridyl-2-pyrazine(L2R/L2s))as the first ligand and Potassium dihydrobis(pyrazol-1-yl)borate (KH2bpz2) as the second ligand, four novel chiral Fe(II) complexes, namely L1RFe(H2bpz2)2 (18), L1SFe(H2bpz2)2 (19), L2RFe(H2bpz2)2 (20) and L2sFe(H2bpz2)2 (21), are successfully synthesized. The corresponding characterization has been performed by elemental analysis, IR, TGA, powder/X-ray single crystals diffraction analysis, magnetic measurements and ferroelectric. According to the molecular structure, there are little difference between 18 and 20, probably induce the different magnetic properties. The spin crossover was observed in 20 and 21 with transition temperature T1/2↓=187 K, T1/2↑=189 K, while antiferromagnetic coupling interactions between complexes 18 and 19. The dielectric anomaly was observed in 20 and 21 at about 213 K, while complexes 18 and 19 did not reflect that. This result can provide an effective approach and theoretical basis to the construction of multifunctional crystalline materials with technologically important properties.